Austin Blackmon, Boston's environment chief, says urban centers, which are home to half the world's population and two-thirds of energy use and emissions, have a critical role to play -- especially since President Trump announced plans to withdraw from the Paris climate agreement.

"Upholding the tenets of the Paris agreement was just too important for us to not move forward, and so we decided to host an international convening on climate here in Boston in the summer of 2018," Blackmon said.

Planning for the summit in Boston is still in the early stages. A date and venue haven't yet been chosen.

Correction: An earlier version of this story said the climate summit announced during the Obama-era had been scheduled for last summer. It was scheduled for the summer of 2017. We regret the error.